Torque-limiting screwdrivers

ABSTRACT

Various torque-limiting screwdrivers, systems, and methods are disclosed. The screwdriver can include a body supporting a motor configured to rotate a screw engaged with the screwdriver. The screwdriver can include a controller configured to implement torque-limiting functionality, such as by monitoring the amount of torque applied to the screw and reducing or stopping rotation of the screw when certain torque-limiting criteria are met. Some embodiments include a threshold point, after which the torque-limiting functionality can be engaged. Some embodiments include a slowdown point, after which the rotational speed of the screw is reduced.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/856,557, filed Jul. 19, 2013; U.S. Provisional Application No.61/872,427, filed Aug. 30, 2013; U.S. Provisional Application No.61/937,346, filed Feb. 7, 2014; and U.S. Provisional Application No.61/940,197, filed Feb. 14, 2014. The entirety of each of theaforementioned applications is incorporated by reference herein.

BACKGROUND

1. Field

This disclosure relates to torque-limiting devices, and in particular toembodiments of torque-limiting screwdrivers.

2. Certain Related Art

Various surgical procedures include inserting one or more screws into abone to retain a structure, such as a plate, on the bone. Duringinsertion, the screw is threaded into a bone and penetrates into thebone. With continued rotation, the screw seats on the plate, such as bya head of the screw contacting the plate. Still further rotation of thescrew secures the screw against the plate and/or further into the bone.However, such further rotation of the screw may cause the screw to stripin the bone, thereby reducing the securement of the screw and the plate.

SUMMARY

It can be beneficial to avoid, or at least inhibit, stripping of thesurgical screw in the bone. This can be accomplished with a screwdriverthat monitors the torque applied to the screw and stops or reduces therotation of the screw when certain torque criteria are satisfied. Forexample, the criteria can include the amount of torque being applied,how the torque is changing over time (e.g., whether the torque isconsistently or inconsistently increasing or decreasing), and whether athreshold has been met. The threshold can aid in determining whether thetorque being sensed is indicative of the screw being secured against theplate or something else, such as a transitory spike in the torque causedby a localized region of harder bone or otherwise.

Moreover, it can be beneficial to reduce the rotating speed of the screwafter certain conditions are satisfied. This can reduce the angularmomentum of the screw and/or components of the screwdriver, and thus canreduce the likelihood of unintentional rotation caused by such momentum,even after active driving of the screw has ceased, which can increasethe chance of the screw stripping in the bone. Furthermore, reducing therotational speed of the screw can increase the amount of time availablefor sensing operations to occur per rotation of the screw. This canfacilitate more precise and accurate monitoring of the rotationalposition of the screw and/or the torque being applied to the screw.

Accordingly, for the reasons indicated above and other reasons, severalembodiments of screwdrivers are disclosed. Typically, the screwdriverincludes a body and a motor. The motor is operably connected to a drivehead at a distal end of the screwdriver such that the motor can turn thedrive head. The drive head can receive a bit (e.g., a crosshead bit,flathead bit, star bit (e.g., Torx), socket bit, or otherwise) that canbe interfaced with a screw having a head with a corresponding shape.Thus, the screw can be positioned at a desired insertion location on asubstrate (e.g., a bone) and the motor can be operated to drive thescrew into the substrate. Various embodiments of the screwdriver canlimit and/or control torque applied to the screw. Certain embodimentsreduce the speed of the screw during the insertion process. Variousembodiments provide one or more of the advantages described above, ornone of them.

Any of the structures, materials, steps, or other features disclosedabove, or disclosed elsewhere herein, can be used in any of theembodiments in this disclosure. Any structure, material, step, or otherfeature of any embodiment can be combined with any structure, material,step, or other feature of any other embodiment to form furtherembodiments, which are part of this disclosure.

None of the preceding summary, the following detailed description, andthe associated drawings purport to limit or define the scope ofprotection. The scope of protection is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The abovementioned and other features of the embodiments disclosedherein are described below with reference to the drawings of theembodiments. The illustrated embodiments are intended to illustrate, butnot to limit the embodiments. Various features of the differentdisclosed embodiments can be combined to form further embodiments, whichare part of this disclosure.

FIG. 1 schematically illustrates an example embodiment of atorque-limiting screwdriver.

FIG. 2 schematically illustrates various stages in the process ofinserting a screw into a bone.

FIG. 2A illustrates an example plot of torque as a function of time orrevolutions during insertion of a screw into a bone.

FIG. 2B illustrates the relationship of the stages of FIG. 2 to the plotof FIG. 2A.

FIG. 3 illustrates a plot of example torques on 3 mm, 4 mm, and 5 mmscrew types as a function of bone density.

FIG. 4 illustrates a torque plot with comparative torque regions.

FIG. 5 illustrates a torque plot with threshold and slowdown points.

FIG. 6 illustrates a process of monitoring and controlling torque duringa screw driving operation.

FIG. 7 illustrates a torque plot with a zone of tolerance.

FIG. 8 illustrates a close-up view of an example torque apex.

DESCRIPTION OF CERTAIN EMBODIMENTS

Various embodiments of a torque-limiting screwdriver 10 are disclosed.As more fully described below, the screwdriver 10 can determine when tostop a screw being driven into various types of bone so as to avoidstripping the screw in the bone. As shown in FIG. 1, the screwdriverincludes a body 11 (also called a housing) that supports a motor 12. Atransfer assembly 14 (e.g., one or more shafts, gears, etc.) operablyconnects the motor 12 to a drive head 16 at a distal end of thescrewdriver 10 such that the motor 12 can turn the drive head 16. Thedrive head 16 can receive a bit, such as a crosshead bit, flathead bit,star bit (e.g., Torx), socket bit (e.g., hex), or otherwise. The bit inturn can be interfaced with a screw having a head with a correspondingshape. Thus, the screw can be positioned at a desired insertion locationon a substrate (e.g., a bone) and the motor 12 can be operated to drivethe screw into the substrate.

The screwdriver 10 can monitor and/or limit the torque that thescrewdriver 10 is applying to the screw during the insertion process.For example, as described in more detail below, the screwdriver 10 caninclude a sensor 18 that senses the current supplied to the motor 12.The sensor 18 can send such data to a controller 20, which can include aprocessor 22 coupled with a memory 24. Because the current supplied tothe motor 12 can be proportional to the torque applied to the screw, thecontroller 20 can dynamically determine the amount of torque beingapplied to the screw. In certain variants, the controller 20 isconfigured to determine or receive signals indicative of one or more ofthe following data features: current supplied to the motor 12, number ofrevolutions of the screw and/or motor, distance traveled by the screw(e.g., into the bone), speed of the motor 12, or otherwise.

As described in more detail below, various embodiments of thescrewdriver 10 include an algorithm adapted to limit and/or control thetorque applied to the screw. This can enable the screwdriver 10 to beused with different screw sizes and different bone densities. Thealgorithm can be included in the memory 24 as program code 26 that beimplemented on a computer-readable non-transitory medium. The processor22 can execute the program code 26 to perform various operations, suchas determining a torque limit, instructing the motor to cease operation,instructing a power source 28 to reduce and/or stop providing power tothe motor 12, or other operations.

Overview of the Screw Insertion Process (FIGS. 2, 2A, and 2B)

The process of inserting a screw into a bone to secure a plate againstthe bone includes several steps. As shown in FIG. 2, in an initialstage, the screw is positioned through an opening in the plate andadjacent to the bone at the desired insertion location. Also, the screwcan be coupled with the screwdriver 10 discussed above, which can beginrotating the screw relative to the bone. As the screw rotates, it beginsto cut into the bone, which provides space for the screw's body to beinserted. For screws that are self-tapping, the screw can begin to pushmaterial outwardly, thereby creating a path into the bone. To facilitatethis process, the user can apply some axial force to the screw, such asvia the screwdriver 10. As illustrated, during the initial stage, thetorque gradient can exhibit a steep upward (e.g., positive) slope andthe rotational speed of the screw is reduced (e.g., compared to thespeed at no load).

After the initial stage concludes, a first insertion stage begins. Inthe first stage, the screw body moves axially into the bone via the pathcreated in the initial stage. As shown in FIG. 2A, during the firststage, the torque gradient can have a downward (e.g., negative) slopeand the rotational speed of the screw can increase compared to the laterpart of the initial stage.

In the second stage, the screw continues advancing into the bonefollowing the path created by the entry threads. Typically, the screwadvances substantially the entire or the entire thread length of thebody of the screw (less the axial thickness of the plate) into the bone.In some implementations, the torque vs. time (or torque vs. revolutionsof the screw) curve will have a positive torque gradient as the screwadvances the length of the thread.

The third stage begins when the screw head initially seats against theplate. As illustrated, the screw typically has a head that is larger indiameter than at least a portion of the opening in the plate. Thus,during the third stage, the head can contact the plate and inhibit orprevent the screw from passing further through the plate. This canresult in an initial sharp increase of the torque curve. As shown inFIG. 2A, during the third stage, the torque gradient can be upward(e.g., positive). For example, the slope can be less than the slope ofthe initial stage but greater than the slope of the second stage. Incertain implementations, the later part of the third stage, the torquegradient exhibits a flattening (e.g., reaches a plateau) and/or includesa crest, such as a localized maximum torque that is less than the torqueat an inflection point during a fourth stage, which is discussed below.In certain variants, the rotational speed of the screw during the thirdstage is less than the speed during the second stage.

In the fourth stage, the screw is fully seated on the plate, therebyfixedly securing the screw, bone, and plate. This can include the headof the screw being partly or completely received into the opening of theplate and inhibited or prevented from further axial movement into thebone by the plate. As illustrated in FIG. 2A, during the fourth stage,the torque can continue increasing, though at a rate that is less thanthe rate of the third stage. For example, the slope of the curve in thefourth stage can be less than the slope in the third stage (e.g., at theend of the third stage). The torque can reach a peak during the fourthstage, after which the torque begins decreasing. In someimplementations, the rotational speed of the screw in the fourth stageis less than the rotational speed of the screw in the initial, first,second, and third stages.

In an overtorque stage, which can occur after the fourth stage, anadditional amount of torque can be applied to the screw to furthertighten the screw in the bone. This can slightly overtorque the screw inthe bone (e.g., violate a yield strength of the screw and/or the bone).Too much overtorque is undesirable as it can cause the screw to strip.But a relatively small amount can be beneficial, because it can resultin slight deformation of the screw and/or the bone, which can aid inmaintaining the screw in its position, and thus inhibit or prevent theplate from moving relative to the bone. In various implementations, theovertorqueing is accomplished by rotating the screw a final amount. Forexample, the screw can be rotated about one rotation, about ½ of arotation, about ¼ of a rotation, about ⅛ of a rotation, values inbetween, or otherwise. In some embodiments, the amount that the screw isovertorqued is at least 1 Newton centimeter (N-cm) and/or less than orequal to about 5 N-cm.

Certain aspects of the stages of the insertion process are summarizedbelow in Table A:

TABLE A Torque Stage Torque Gradient Speed Observations Initial Stage:Screw Initially no load Steeply High Increasing values. drivinginitiation and and no torque positive Large noise to bone engagementsignal ratio First Stage: Screw Initially high Negative High Decrease oradvancement starts leveling off values Second Stage: Screw Initially lowPositive Reducing Smooth continuous inside bone and increasing valuescontinue advancing Third Stage: Screw Middle Flat to Mid Small plateauor seated on plate positive distinct increase of values Fourth Stage:Screw High Level and/or Low Cresting, plateau of compressing platenegative values against bone Overtorque Stage: High to Middle NegativeLow Decreasing values Screw seated on plate and additional torqueapplied

Typically, to remove the screw from the bone, and to free the plate, thescrewdriver 10 can be interfaced with the head of the screw and therotation of the screw reversed. Because the screw is not cutting intothe bone and is not being tightened against the bone or plate, thetorque on the screw during a removal operation is normally less thanduring the insertion process described above.

Certain Variables that Affect Torque (FIG. 3)

The torque needed to insert the screw in a given bone can varysignificantly. One factor that affects the amount of torque required toinsert the screw into a bone is the density of the bone, which canchange based on age, gender, disease, and other factors. Typically, thedenser the bone, the greater the force required to insert the screw.Another factor that affects the amount of torque required to insert thescrew into a bone is the specifics of the screw, such as the diameter,length, thread type (e.g., shape and/or number of threads per inch),material, coefficient of friction with the bone, and other features.Generally, the longer the screw (e.g., an axial length of at leastabout: 3 mm, 4 mm, 5 mm, or otherwise), the more torque required toinsert the screw to a fully installed position.

FIG. 3 shows illustrative example torques on 3 mm, 4 mm, and 5 mm screwtypes as a function of bone density. As shown, there can be differenttorque requirements based on the size and type of the screw and the bonedensity substrate against which the screw is inserted. This can causeissues in using a fixed torque limit. For example, if the torque limitis fixed based on a dense bone substrate and the smaller (e.g., 3 mm)screw, then a larger (e.g., 5 mm) screw inserted on a denser bonesubstrate may not seat completely. On the other hand, if the torquelimit is fixed based on a larger (e.g., 5 mm) screw and densersubstrate, the smaller (e.g., 3 mm) screw on a less dense substrate maystrip during insertion.

Fixed Torque-Limiting Embodiments

Certain screwdrivers include a fixed torque value for a specific screwtype. For example, for a 3 mm screw, the screwdriver 10 can include atorque limit set at a value that is specific to that type of screw andto the particular type of bone the screw is to be inserted into. For ascrewdriver 10 configured to receive and drive three types of screws(e.g., 3 mm, 4 mm, and 5 mm), the screwdriver 10 would include threetorque limit values. The values can be determined by experimentation foreach screw type with each substrate.

Variable Torque-Limiting Embodiments (FIGS. 4-8)

Various embodiments of the screwdriver 10 use an algorithm todynamically determine the torque limit and/or when to stop rotation ofthe screw. This can allow the screwdriver to account for insertionvariables (e.g., the density of the bone and the screw specifics) so asto correctly seat the screw, while also inhibiting or preventing thescrew from stripping. In several embodiments, the insertion variables donot need to be input into the screwdriver. Rather, certain embodimentsof the screwdriver 10 can determine when the screw is properly installedand/or can avoid stripping of the screw based on the torque required toturn the screw in relation to other parameters, such as the time thatthe screwdriver 10 has been rotating the screw and the amount of torquethat has already been applied to the screw.

Several torque-limiting methods, algorithms, and components aredescribed below. Any method, algorithm, or component disclosed anywherein this specification can be used in conjunction with any other method,algorithm, or component disclosed anywhere in this specification, or canbe used separately.

Differential Torque Comparisons

In some embodiments, the algorithm compares how the torque has changedduring certain portions of the insertion operation. To facilitate thiscomparison, the controller 20 can calculate discreet changes in thetorque during the course of insertion of the screw (e.g., torque as afunction of time). For example, as shown in FIG. 4, the controller 20can determine Δq values and Δt values throughout some or all of theinsertion of the screw, where Δq is the change in torque and Δt is thechange in time, depth, or revolution of the screw. Certain embodimentsuse a relationship of the Δq values and Δt values during the insertionstages of the screw. For example, some implementations engage atorque-limiting feature (e.g., stop the motor) when the followingcomparison is met:

$\frac{\Delta\; q\; 3}{\Delta\; t\; 3} > \frac{\Delta\; q\; 2}{\Delta\; t\; 2} > \frac{\Delta\; q\; 1}{\Delta\; t\; 1}$

Such an algorithm can enable the screwdriver 10 to limit the torquewhile also accounting for certain aspects of the insertion process. Forexample, this algorithm can include and/or consider that the torquestarts at low level and a high level of speed. Certain embodiments ofthe algorithm include and/or consider that, when the screw is beingthreaded into bone, the torque may increase and the reduction in speedmay decrease. Some variants of the algorithm include and/or considerthat, when the screw seats on the plate, the torque may increase and thespeed may decrease. Various embodiments of the algorithm are configuredto inhibit or avoid the failure mode of stripping of the screw.

In certain embodiments, a measured amount of torque (or current drawn bythe motor) is sampled, such as about every 10 milliseconds (ms), 20 ms,or other time values. The torque and time data can be stored in thememory. This can facilitate monitoring the change in the torque relativeto time (e.g., a first derivative of the torque). As noted above, thetorque can be directly proportional to the motor power required toinsert the screw. In several embodiments, the torque at a given time isdetermined by the controller 20, which receives a signal from the sensor18 indicative of the current drawn by the motor 12.

Consecutive Torque Values, Thresholds, and Slowdowns

In some embodiments, the methods and algorithms activate (e.g., engage)torque-limiting functionality when a number of values meet a condition.For example, as discussed in more detail below, the screwdriver 10 canmonitor the torque for a number (e.g., three) of consecutivedecrementing values and can reduce and/or stop rotation of the screw(e.g., by reducing or stopping power to the motor 12) in response tosuch a condition being met.

FIG. 5 shows an illustrative torque versus time curve. As shown, thetorque curve can be divided into several periods, such as Period 1,Period 2, Period 3 and Period 4. In some embodiments, Period 1 (e.g.,the initial stage as discussed above) includes the initial engagementand entry of the screw into a substrate, such as a bone. During thisperiod, the amount of torque can increase rapidly. Period 1 may alsoinclude an increased level of noise and/or unpredictable or unreliabletorque data. As such, in some embodiments, the torque data measuredduring Period 1 is not used to control operation of the driver. Rather,the torque data during Period 1 is ignored or recorded only. Period 1 isthus referred to as a “deadband.” In some embodiments, the deadbandextends for at least about 50 ms and/or less than or equal to about 200ms after Time 0 (e.g. the beginning of the screw insertion process atwhich the screw begins penetrating into the bone). In certainembodiments, the deadband has a duration of less than or equal to about100 ms.

Period 2 occurs at the conclusion of Period 1. During Period 2 (e.g.,the second stage as discussed above), the screw is in the process ofthreading into the substrate and may experience less torque than theinitial torque experienced during Period 1. In some variants, the torquedata of Period 2 is not used for torque-limiting purposes but isrecorded or logged.

In Period 3 (e.g., similar to the third stage and about the first halfof the fourth stage discussed above), the torque on the screw canincrease. This is because, for example, the screw engages a plate, andbegins tightening the plate against the bone. In some embodiments, athreshold point (e.g., threshold condition) is reached during insertionof the screw, such as at or near the beginning of Period 3. In someembodiments, the screwdriver 10 renders torque-limiting functionalityactivatable in response to reaching the threshold point. For example, ifa torque-limiting condition is experienced prior to reaching thethreshold point, the torque-limiting functionality is not activated. Incomparison, after the threshold point has been reached, if atorque-limiting condition occurs, then the torque-limiting functionalitycan be activated. This can avoid erroneous and/or transitory torquevalues activating the torque-limiting functionality, which could resultin premature stopping of the screwdriver 10 and/or incomplete insertionof the screw. In certain implementations, the threshold point can act asa gate, whereby the torque-limiting functionality can be engaged only ator after the torque applied to the screw reaching the threshold point.

In some embodiments, the threshold point is a function of torque and/orcurrent. For example, threshold point can be a torque value of at leastabout: 5 N-cm, 7 N-cm, 10 N-cm, 12 N-cm, 15 N-cm, 17 N-cm, 20 N-cm, 25N-cm, values between the aforementioned values, or other values. Incertain variants, the threshold point occurs at a torque of greater thanor equal to about 5 N-cm and/or less than or equal to about 15 N-cm. Insome embodiments, in response to the torque applied to the screwmeeting, or exceeding, the torque value of the threshold point, then thetorque-limiting functionality is able to be engaged. As noted above, thetorque can be determined from the current drawn by the motor 12. In someembodiments, the threshold point is met or exceeded when the electricalcurrent drawn by the motor 12 is at least about: 0.25 A, 0.50 A, 0.75 A,1 A, 1.25 A, 1.5 A, 1.75 A, 2 A, 2.5 A, 3 A, values between theaforementioned values, or other values. In certain implementations thatinclude a polyphase motor (e.g., a 3-phase motor), the average totalforward current of the phases is used in determining the current. Someimplementations use a direct-quadrature-zero transformation or Park'sTransformation in determining the current.

In some embodiments, the threshold point is a function of time. Forexample, in certain variants, the threshold point occurs a certainamount of time from Time 0. In some embodiments, the threshold pointoccurs at least about 300 ms and/or less than or equal to about 500 msfrom Time 0. In certain variants, the threshold point occurs at greaterthan or equal to about 200 ms after Time 0.

With continued reference to FIG. 5, the screwdriver 10 can include aslowdown point (e.g., a slowdown condition). In some embodiments, thescrewdriver 10 changes the speed at which it rotates the screw inresponse to the slowdown point being, or having been, reached. Forexample, prior to reaching the slowdown point, the screwdriver 10 mayoperate at first speed (e.g., greater than or equal to about 3600 rpm)and after reaching the slowdown point, the screwdriver 10 can operate ata second rotational speed (e.g., less than or equal to about 900 rpm).In some embodiments, the slowdown results in a delay of the fullinsertion of the screw of at least about: 0.10 second, 0.25 second, 0.50second, 0.75 second, 1 second, 1.5 seconds, values between theaforementioned values, or other values. Certain implementations of thescrewdriver 10 can increase the total time it takes to insert the screw,such as by at least the aforementioned time values. Otherimplementations of the screwdriver 10 do not increase the totalinsertion time. For example, some variants increase the insertion speed(and reduce the insertion time) before the slowdown point a sufficientamount to counteract the reduction in speed (and increase in insertiontime) after the slowdown point.

Reducing the insertion speed (e.g., rotational speed) of the screw canbe beneficial. For example, this can reduce the rate at which the torqueincreases during insertion of the screw. In some embodiments, reducingthe insertion speed improves monitoring and/or resolution of the torqueapplied to the screw by the screwdriver 10 during the screw insertionprocess (e.g., during Period 3 and/or Period 4), such as by providingadditional time for the processor 22 and/or sensor 18 (e.g., currentsensor) to monitor the amount of torque on the screw and/or to determinewhether the torque-limiting functionality should be activated. Forexample, a reduction in the speed from about 3600 rpm to about 900 rpmcan increase the duration of Period 3 and/or Period 4 by a factor ofabout 4. In some embodiments, the slowdown results in an increase inresolution of the monitored torque (e.g., of the motor's current drawdetected by the sensor 18) of at least about: 2, 3, 4, 5, 6, valuesbetween the aforementioned values, or other values.

In some implementations, the reduction in rotational speed can provide amore accurate and/or precise rotation of the screw relative to thesubstrate. For example, a reduction in the rotational speed of themotor, drive train and/or screw can reduce the momentum of thosecomponents. In some embodiments, this can reduce the likelihood oferror, such as error caused by unintended rotation from that momentum.In some embodiments, the slowdown results in the rotational momentum ofthe screw being reduced at least about: 50%, 100%, 200%, 300%, 400%,500%, values between the aforementioned values, or other values.

In certain variants, the reduction in speed of the screw can provide anindication to a user, such as a surgeon. For example, the reduction canprovide a signal that a certain amount of torque has been reached, thatthe threshold point has been or is about to be reached (e.g., withinless than or equal to about 0.75 second), that the torque-limiting pointis about to be reached (e.g., within less than or equal to about 1second), and/or that the screwdriver 10 is about to stop driving thescrew. In some embodiments, the slowdown is accompanied by an indicator,such as the activation of a light (e.g., an LED), an audible sound, orother sensory indicator.

In some embodiments, the slowdown point is a function of torque and/orcurrent. For example, slowdown point can be a torque value of at leastabout: 5 N-cm, 7 N-cm, 10 N-cm, 12 N-cm, 15 N-cm, 17 N-cm, 20 N-cm, 25N-cm, values between the aforementioned values, or other values. Incertain implementations, the slowdown point occurs at a torque ofgreater than or equal to about 5 N-cm and/or less than or equal to about15 N-cm. In some embodiments, the screwdriver 10 engages thespeed-reduction functionality in response to the torque on the screwmeeting, or exceeding, the torque value of the slowdown point. Aspreviously discussed, the torque can be determined from the currentdrawn by the motor 12. In some embodiments, the slowdown point isreached when the electrical current drawn by the motor 12 is at leastabout: 0.25 A, 0.50 A, 0.75 A, 1 A, 1.25 A, 1.5 A, 1.75 A, 2 A, 2.5 A, 3A, values between the aforementioned values, or other values. Someimplementations that include a polyphase motor (e.g., a 3-phase motor)use the average total forward current of the phases in determining thecurrent. Certain variants use a direct-quadrature-zero transformation orPark's Transformation in determining the current.

In some embodiments, the slowdown point is a function of time. Forexample, in certain variants, the slowdown point occurs a certain amountof time from Time 0. In some embodiments, the slowdown point occurs atleast about 300 ms and/or less than or equal to about 500 ms from Time0. In certain variants, the slowdown point occurs at greater than orequal to about 200 ms after Time 0.

In some embodiments, the threshold point and the slowdown point are thesame point. For example, as shown, both the threshold point and theslowdown point can occur at the beginning of Period 3. In someimplementations, this is determined by an amount of time from Time 0,such as at least about: 150 ms, 200 ms, 250 ms, 300 ms, 350 ms, 400 ms,500 ms, values between the aforementioned values, or other values. Inother embodiments, the threshold point and the slowdown point aredifferent points. For example, in some embodiments the slowdown pointoccurs before the threshold point; in other embodiments the slowdownpoint occurs after the threshold point. In some implementations, thethreshold point and the slowdown point are separated by an amount oftime (e.g., less than or equal to about 100 ms). In some embodiments,the threshold point and the slowdown point are separated by an amount oftorque (e.g., less than or equal to about 3 N-cm).

As illustrated, Period 4 (e.g., similar to about the second half of thefourth stage and the overtorque stage discussed above) begins afterPeriod 3 ends, such as at about the apex of the torque curve. Period 4can include a decrease in the torque (e.g., a negative torque gradient).This can suggest that yielding and/or stripping of the screw and/or thesubstrate is imminent or has begun. In some embodiments, the screwdriver10 monitors the torque data for N consecutive decreasing torque values.For example, in some implementations, N equals 2, 3, 4, 5, 6, 7, orotherwise. In an embodiment in which N is 4, the torque-limitingcondition would be satisfied when 4 consecutive decreasing torque valuesare observed. In various embodiments, after the torque-limitingcondition has been satisfied and the threshold point has been passed,the torque-limiting algorithm can instruct that the screwdriver 10 ceaseturning the screw. For example, power to the motor 12 can be reduced oreliminated.

FIG. 6 illustrates another embodiment of a torque-limiting method andalgorithm. In this algorithm:

t is the time increment in microseconds;

I is the current sampling;

Γ is the torque, which is proportional to the current sample;

i is the time increment of the system sample;

n is the array length;

Q is dΓ/t; and

S is a count variable.

The algorithm can include arrays, such as:

${\overset{\_}{Q}}_{A} = {\begin{matrix}{\Gamma_{i}\mspace{14mu}\ldots\mspace{14mu}\Gamma_{n}} \\{t_{i}\mspace{14mu}\ldots\mspace{14mu} t_{n}}\end{matrix}}$ ${\overset{\_}{Q}}_{B} = {\begin{matrix}{\Gamma_{i + 1}\mspace{14mu}\ldots\mspace{14mu}\Gamma_{n + 1}} \\{t_{i + 1}\mspace{14mu}\ldots\mspace{20mu} t_{n + 1}}\end{matrix}}$

As illustrated, in a first block 601, the motor 12 can be started. Forexample, in response to a user activating an input (e.g., a button orswitch), the controller 20 on the screwdriver 10 can instruct that powerbe supplied to the motor 12 to begin turning the screw. In someembodiments, the motor 12 continues to run in at least a second block602.

In various embodiments, torque values are collected (e.g., observed andrecorded). In this regard, various embodiments detect (e.g., with asensor 18) the amount of current being drawn by the motor 12. Thiscurrent draw data can be used to determine the amount of torque becausethe current drawn by the motor 12 is generally proportional to theamount of torque that the motor is applying to a screw being driven bythe screwdriver 10. As shown, in block 603, a torque amount at each timeincrement can be collected and stored in the memory 24. This torque andtime data can be used to create an array or matrix Q_(A) for i through nsample increments. In a subsequent block 604, further torque values canbe collected for additional time increments, and that further time andtorque data can be used to create another array or matrix Q_(B).

Some embodiments include a comparison block 605, in which Q_(A) andQ_(B) are compared. In certain implementations, if Q_(B) is greater thanQ_(A), then the algorithm returns to an earlier block, such as block602. This can allow additional arrays Q_(A) and Q_(B) to be created andcompared. Accordingly, in some embodiments, the comparison of arraysQ_(A) and Q_(B) is substantially constantly occurring in a loop duringimplementation of the algorithm.

As illustrated, if Q_(B) is not greater than Q_(A), then an iterativeportion of the algorithm can be performed. In some embodiments, thisincludes initializing and/or incrementing a count variable S. Forexample, for each time the algorithm determines that Q_(B) is notgreater than Q_(A), then the algorithm can proceed to block 606, inwhich the count variable S is increased by 1.

As shown, in block 607, the count variable S is compared to a presetnumber N of allowable consecutive decreasing torque values (e.g., 2, 3,4, 5, 6, or otherwise). For example, if the count variable S is notgreater than the number N, then the algorithm can return back to anearlier block (e.g., block 602). Additional Q_(A) and Q_(B) arrays canbe created and compared in blocks 603-605. On returning to block 605, ifQ_(B) is still not greater than Q_(A), then the algorithm can proceed toblock 606 and the count variable S is increased by 1 again. In variousembodiments, if Q_(B) is greater than Q_(A), then the count variable Sis initialized (e.g., S=0).

In certain embodiments, if the count variable S is greater (or greaterthan or equal to in some variants) than N consecutive decreasing torquevalues, then the algorithm proceeds to block 608, in which atorque-limiting function can be activated. For example, the controller20 can issue an instruction that the motor 12 should be stopped (e.g.,by eliminating or reducing the power supplied to the motor). Thus, thetorque being applied to the screw can be controlled and/or limited.

According to various embodiments, if fewer than N consecutive decreasingtorque values are observed, the motor 12 continues to operate. This canreduce the likelihood that the torque-limiting algorithm willprematurely stop the driving of the screw. For example, by not stoppingthe motor 12 unless at least N consecutive decreasing torque values areobserved, premature stoppage of the motor due to noise in the currentsignal or transitory torque reductions can be avoided.

In some embodiments, if the count variable S is greater than or equal toa preset number N of consecutive decreasing torque values, then themotor is stopped. For example, if N equals 4, then the motor is stoppedwhen the count variable S is greater than or equal to 4 (e.g., fourconsecutive iterations through blocks 602-606 in which the torque valuesdecrease each time). Otherwise, in some embodiments, the motor continuesrunning and driving the screw.

Zone of Tolerance and Peak Determination

FIGS. 7 and 8 illustrate a further torque-limiting method and algorithm.As shown, certain embodiments include a “zone of tolerance” prior to andafter the apex of the torque curve. Stopping the rotation of the screwin the zone of tolerance can provide confidence that the screw issecured in the bone (e.g., the screw has not been stripped-out).

As shown in FIG. 7, the zone of tolerance can include an inflectionpoint (e.g., the slope changes becomes zero, changes from positive tonegative, or otherwise). In some embodiments, the inflection point is intwo dimensions, such as torque and time (or revolutions of the screw).Certain implementations of the screwdriver 10 monitor for and/or issue astop instruction based on the inflection point having been reached. Thiscan enable the screwdriver 10 to stop the motor 12 near, at, or afterthe inflection point has been reached. In some variants, the motor 12 ispartially or completely stopped after the inflection point has beenreached and an additional event has occurred. For example, the event canbe an amount of torque change (e.g., a torque reduction of at leastabout: 5%, 10%, 20%, 30%, values between the aforementioned values, orother values), a rotation of the screw occurs (e.g., an additionalrotation of at least about: ⅛ turn, ¼ turn, ½ turn, ¾ turn, 1 turn, 2turns, values between the aforementioned values, or other values), orotherwise.

In some embodiments, the controller 20 determines the zone of toleranceby monitoring the torque for a number of consecutive increasing torquevalues and a number of consecutive decreasing torque values. Forexample, the controller 20 can determine when N1 (e.g., 2, 3, 4, 5, 6,7, etc.) consecutive increasing values have occurred, followed by N2(e.g., 2, 3, 4, 5, 6, 7, etc.) consecutive decreasing values. This canindicate that the peak has been reached and that the torque-limitingfunctionality should be engaged. In some embodiments, one or more torquevalues separate the consecutive increasing values and the consecutivedecreasing values. For example, the torque-limiting functionality can beengaged in response to N1 consecutive increasing values can be detected,followed by one or more interim torque values, followed by N2consecutive decreasing values. This can account for slight variations inthe torque at or near the peak and/or for substantially equal peaktorque values.

The zone of tolerance can be further seen FIG. 8's close-up view of anexample torque apex. As illustrated, the zone of tolerance can include apositive slope portion (also called the upslope portion), a negativeslope portion (also called the downslope portion), or both sides ofslope. In some embodiments, the torque-limiting algorithm considers boththe upslope portion and downslope portion during the screw insertionprocess. In certain embodiments, the upslope portion of the algorithmfacilitates or ensures securing of the screw, while the downslopeportion of the algorithm facilitates or ensures that the screwdriverceases turning the screw after the torque has reached an apex.

Certain embodiments determine the upslope by determining the change intorque over change in time (Δq/Δt) values during the insertionoperation. The method can also include measuring X number (e.g., 2, 3,4, 5, 6, or otherwise) of torque data points. The method can includerotating the screw and monitoring the torque value until the torquevalue reaches the peak (e.g., apex). For example, the peak can bedetermined by comparing Δq/Δt values at different torque sampling points(e.g., 0, 1, 2, 3, 4), such as can be expressed as: Δq(p0)/Δt,Δq(p1)/Δt, Δq(p2)/Δt, Δq(p3)/Δt, Δq(p4)/Δt, etc. In some embodiments,the peak (e.g., when the value of Δq/Δt has reached its maximum value)indicates that the screw is secured in place and has compressed the boneplate against the bone. If the Δq/Δt value is at or near zero, then thiscan indicate that the screw is secured and/or is at or near the peaktorque. As such, in certain embodiments, in response to the Δq/Δt valuebeing at or near zero, screw rotation is stopped (e.g., by stopping themotor 12).

Similarly, certain embodiments determine the downslope by determiningthe change in torque over change in time (Δq/Δt) values during theinsertion operation. However, in using the downslope to determine thepeak torque, the Δq/Δt comparison looks for Δq/Δt values that are zeroor slightly decreasing (e.g., less than about 5% of the previous value)for N number of consecutive points.

Override Functionality

Some embodiments of the screwdriver 10 allow a user to override thetorque limitation determined by the controller 20. This can bebeneficial (e.g., if the screw happens to stop before seating on theplate) by permitting the user to override the stoppage of the screw. Inseveral embodiments, the screwdriver 10 includes an override input, suchas a switch, button, or the like. The override input can be configuredto send an override signal to the controller 20, which overrides thecontroller's stoppage of the screwdriver's turning of the screw.

As noted above, certain embodiments of the override input can facilitateseating the screw against the plate. Sometimes, when placing the screw,the screw head remains “proud” of the bone plate (e.g., a bottom surfaceof the head of the screw remains spaced apart from a top and/or matingsurface of the plate). This can result in a less secure mounting of theplate relative to the bone, can inhibit or prevent healing, and/or cancause the patient discomfort. To aid in remedying a proud screw, or forother reasons, the override input can allow a user to rotate the screwan incremental amount, thereby further driving the screw into the boneand more fully (or completely fully) seating the screw on the plate. Incertain implementations, the override input momentarily overrides thetorque-limiting feature and allows some or all available power to go tothe motor 12 to execute the incremental turn. In various embodiments,activation of the override input provides an additional incrementalrotational movement of the screwdriver bit of at least about: 45°, 90°,135°, 180°, 270°, 360°, 540°, 720°, values between the aforementionedvalues, or otherwise.

In certain embodiments, the override functionality can be engagedwhenever the override input is activated (e.g., depressed). For example,some embodiments allow an override for each activation of the overrideinput and/or do not limit the number overrides permitted. In certainimplementations, only a limited number of overrides are allowed. Forexample, some embodiments only allow one override, after whichadditional override inputs are ignored. In some embodiments, theoverride input is configured to rotate the screw a predetermined amount(e.g., 1 revolution, ½ revolution, ¼ revolution, values in between, orotherwise), for each activation of the override input.

According to some variants, activation of the override input allowsoverride operation of the screwdriver 10 for a period of time withoutrequiring additional activation of the override input. This canfacilitate convenient operation of other inputs (e.g., controls to drivethe screw forward or in reverse) during the override period without theneed to repeatedly activate the override input. For example, an overridebutton or other input device can be depressed or otherwise activated toinitiate the override time period, during which one or many operationscan be performed that would otherwise be inhibited or prevented (e.g.,because of the torque-limiting features described above). In someembodiments, the override time period can be at least about: 5 seconds,10 seconds, 30 seconds, 1 minute, 2 minutes, 5 minutes, values betweenthe aforementioned values, or otherwise.

A variety of override input devices and methods for activating and/orotherwise controlling the override feature are contemplated. Forexample, in certain embodiments, the override feature is activated byengaging (e.g., pressing and/or holding) a button, or combination ofbuttons. Some variants include a dedicated button that activates theoverride feature. Certain embodiments of the override input deviceinclude a switch, rocker, slide, proximity sensor, touch screen, orotherwise. Various embodiments can provide feedback (e.g., tactilevisual and/or audible) to the user.

Several implementations include an adjustable override input device thatcan be moved to a plurality of positions to provide different overridefunctionality. For example, the input device can comprise a button,slider, or switch with multiple positions, each with a differentoverride function, such as different operations that are permittedand/or different override time periods.

In some embodiments, the adjustable override input device comprises awheel or dial that can be rotated between various positions. Forexample, the wheel or dial can have several (e.g., two, three, four,five, six, or more) positions located a rotational distance apart, suchas at least about 45° apart or at least about 90° apart. The screwdriver10 can be configured to detect the position of the dial or wheel and toprovide an incremental rotation of the screwdriver bit or the motor 12that is about equal to, less than, greater than, or otherwise related tothe incremental rotation of the dial or wheel. In certain variants, theincremental rotation of the screwdriver bit is proportional to therotation of the wheel or dial. In some various embodiments, whilerotating the wheel or dial, the user receives tactile or audiblefeedback, such as distinct “clicks” or detents, such as at each 90°increment.

Certain embodiments have a dial or wheel with multiple positions. Forexample, the wheel can have three positions that are each located about90° apart. In some such embodiments, when the dial or wheel ispositioned in the first position then the screwdriver 10 will provide afirst incremental rotation (e.g., about 90°). When the dial or wheel ispositioned in the second position then the screwdriver will provide asecond incremental rotation (e.g., about 180°). When the dial or wheelis positioned in the third position then the screwdriver will provide athird incremental rotation (e.g., about 270°).

In some embodiments, the override input device controls the direction ofrotation of the bit of the screwdriver 10. This can allow the overrideinput device to control whether the screw is being driven forward or inreverse. In certain variants, the screwdriver 10 drives the screwforward when the override input device is in a first position andreverses the screw when the override input device is in a secondposition. In some implementations, the override input device is a wheelor dial, and the rotational direction of the screwdriver bit is the sameas the direction that the wheel or dial is rotated.

Other Features

Various embodiments of the screwdriver 10 have a variety of operationalcharacteristics. For example, some embodiments provide a maximumrotational speed (at no load) of at least about: 3,000 rpm, 4,000 rpm,5,000 rpm, 6,000 rpm, 10,000 rpm, values between the aforementionedvalues, or other values. As noted above, some embodiments slow therotation of the screw after a slowdown point has been reached. Certainsuch embodiments have a slowed speed (at no load) of less than or equalto about: 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1,000 rpm, 1,100rpm, 1,200 rpm, values between the aforementioned values, or othervalues. Certain implementations of the screwdriver 10 can provide atorque on the screw of at least about: 25 in-ozs, 30 in-ozs, 35 in-ozs,40 in-ozs, 45 in-ozs, values between the aforementioned values, or othervalues. Some embodiments of the screwdriver 10 can provide a torque onthe screw of at least about: 25 N-cm, 30 N-cm, 35 N-cm, 40 N-cm, 45N-cm, values between the aforementioned values, or other values.

The screwdriver 10 can be implemented with various types of motors. Insome variants, the motor 12 is powered by a power source, such as asource of AC or DC electrical power. In some embodiments, the motor 12is powered by an on-board power source, such as a battery, capacitor, orotherwise. In some embodiments, the motor 12 is configured to receivepower from an external source, such as from a console, wall socket, orother external power source. In some embodiments, the motor 12 is abrushless DC motor. In some embodiments, the motor 12 is a three-phaseelectric motor. The motor 12 can include one or more hall sensors, whichcan send signals to the controller 20 to enable the controller 20 todetermine the number of revolutions of the motor 12. In certainvariants, the controller 20 determines the number of revolutions of thescrew from the number of revolutions of the motor 12.

Some implementations are configured to stop the rotation of the screw byshutting-off (e.g., substantially or totally) the power to the motor 12.Certain implementations include a brake to actively decelerate the motoror components. For example, some implementations include a friction orelectromagnetic brake.

Various embodiments of the screwdriver 10 include a forward input that auser can engage to instruct the screwdriver 10 to turn the screw in aforward direction, such as in the direction to insert the screw into thebone. For example, the forward input can be a switch, button, dial,trigger, slider, touchpad, or the like. Certain embodiments havemultiple input members, such as a fast forward switch (e.g., the motorwill spin at about 4100 RPM at no-load) and a slow forward switch (e.g.,motor will spin at 500 RPM at no-load). Some implementations have areversing input, which can instruct the screwdriver 10 to turn the screwin a reverse direction, such as in the direction to remove the screwfrom the bone. The reversing input can be similar to the forward input,such as the options described above. In some embodiments, engaging thereversing input causes the motor to spin at about 500 RPM at no-load. Incertain implementations, the final rotational speed of the screw isabout 500 RPM. In some embodiments, the forward input and the overrideinput are the same component.

In various embodiments, the screwdriver 10 includes componentsconfigured to adjust the torque data, such as by filtering the torquedata, decreasing noise in a signal from a sensor 18 (e.g., a motorcurrent sensor), or otherwise. For example, the screwdriver 10 caninclude one or more low-pass filters. The filters can be implemented inhardware and/or software. For example, in some embodiments, the filterscomprise resistance capacitor circuitry. Certain embodiments include asoftware filter configured to filter out certain frequencies and/orlevels of torque data. In various embodiments, the filtering componentscan facilitate a smoother torque curve. In some variants, the filteringcomponents can reduce errors in the torque-limiting functionality thatmay otherwise be caused by noise and/or outlier measurements.

Summary

Various torque-limiting screwdriver systems and methods have beendisclosed in the context of aspects of certain embodiments, examples,and variations. Nevertheless, the present disclosure extends beyond thespecifically disclosed embodiments, examples, and variations to otheralternative embodiments and/or uses of the invention, as well as obviousmodifications and equivalents thereof. In addition, while a number ofvariations of the screwdriver have been shown and described in detail,other modifications, which are within the scope of this disclosure, willbe readily apparent to those of skill in the art based upon thisdisclosure.

Certain features have been described in the context of separateimplementations can also be implemented in combination in a singleimplementation. Conversely, various features that are described in thecontext of a single implementation can also be implemented in multipleimplementations separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations, one or more features from a claimed combination can, insome cases, be excised from the combination, and the combination may beclaimed as any subcombination or variation of any subcombination.

Any portion of any of the steps, processes, structures, and/or devicesdisclosed or illustrated in one embodiment, flowchart, or example inthis disclosure can be combined or used with (or instead of) any otherportion of any of the steps, processes, structures, and/or devicesdisclosed or illustrated in a different embodiment, flowchart, orexample. The embodiments and examples described herein are not intendedto be discrete and separate from each other. Combinations, variations,and other implementations of the disclosed features are within the scopeof this disclosure.

Any of the steps and blocks can be adjusted or modified. Other oradditional steps can be used. None of the steps or blocks describedherein is essential or indispensable. Moreover, while operations may bedepicted in the drawings or described in the specification in aparticular order, such operations need not be performed in theparticular order shown or in sequential order, and that all operationsneed not be performed, to achieve desirable results. Other operationsthat are not depicted or described can be incorporated in the examplemethods and processes. For example, one or more additional operationscan be performed before, after, simultaneously, or between any of thedescribed operations. Further, the operations may be rearranged orreordered in other implementations. Also, the separation of varioussystem components in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described components and systems cangenerally be integrated together in a single product or packaged intomultiple products.

Some of the devices, systems, embodiments, and processes usecontrollers, which can include a processor and memory. Each of theroutines, processes, methods, and algorithms described above may beembodied in, and fully or partially automated by, code modules executedby one or more computers, computer processors, or machines configured toexecute computer instructions. The code modules may be stored on anytype of non-transitory computer-readable storage medium or tangiblecomputer storage device, such as hard drives, solid state memory, flashmemory, optical disc, and/or the like. The processes and algorithms maybe implemented partially or wholly in application-specific circuitry.The results of the disclosed processes and process steps may be stored,persistently or otherwise, in any type of non-transitory computerstorage such as volatile or non-volatile storage.

Conditional language used herein, such as, “can,” “could,” “might,”“may,” “e.g.,” and the like, unless specifically stated otherwise, orotherwise understood within the context as used, is generally intendedto convey that certain embodiments include, while other embodiments donot include, certain features, elements and/or steps. Thus, suchconditional language is not generally intended to imply that features,elements and/or steps are in any way required for one or moreembodiments or that one or more embodiments necessarily include logicfor deciding, with or without author input or prompting, whether thesefeatures, elements and/or steps are included or are to be performed inany particular embodiment.

Conjunctive language, such as the phrase “at least one of X, Y, and Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to convey that an item, term, etc. may beeither X, Y, or Z. Thus, such conjunctive language is not generallyintended to imply that certain embodiments require at least one of X, atleast one of Y, and at least one of Z to each be present.

The terms “comprising,” “including,” “having,” and the like aresynonymous and are used inclusively, in an open-ended fashion, and donot exclude additional elements, features, acts, operations and soforth. Also, the term “or” is used in its inclusive sense (and not inits exclusive sense) so that when used, for example, to connect a listof elements, the term “or” means one, some, or all of the elements inthe list. The term “and/or” means that “and” applies to some embodimentsand “or” applies to some embodiments. Thus, A, B, and/or C is equivalentto A, B, and C written in one sentence and A, B, or C written in anothersentence. The term “and/or” is used to avoid unnecessary redundancy.

The terms “approximately,” “about,” and “substantially” as used hereinrepresent an amount close to the stated amount that still performs adesired function or achieves a desired result. For example, in someembodiments, as the context may dictate, the terms “approximately”,“about”, and “substantially” may refer to an amount that is within lessthan or equal to 10% of the stated amount. The term “generally” as usedherein represents a value, amount, or characteristic that predominantlyincludes or tends toward a particular value, amount, or characteristic.As an example, in certain embodiments, as the context may dictate, theterm “generally parallel” can refer to something that departs fromexactly parallel by less than or equal to 20 degrees.

Terms relating to circular shapes as used herein, such as diameter orradius, should be understood not to require perfect circular structures,but rather should be applied to any suitable structure with across-sectional region that can be measured from side-to-side. Termsrelating to shapes, such as “circular” or “cylindrical” or“semi-circular” or “semi-cylindrical” or any related or similar terms,are not required to conform strictly to the mathematical definitions ofcircles or cylinders or other structures, but can encompass structuresthat are reasonably close approximations. Likewise, shapes modified bythe word “generally” (e.g., “generally cylindrical”) can includereasonably close approximations of the stated shape.

Some embodiments have been described in connection with the accompanyingdrawings. The figures are drawn to scale, but such scale should not belimiting, since dimensions and proportions other than what are shown arecontemplated and are within the scope of this disclosure. Distances,angles, etc. are merely illustrative and do not necessarily bear anexact relationship to actual dimensions and layout of the devicesillustrated. Components can be added, removed, and/or rearranged.Further, the disclosure herein of any particular feature, aspect,method, property, characteristic, quality, attribute, element, or thelike in connection with various embodiments can be used in all otherembodiments set forth herein. Additionally, it will be recognized thatany methods described herein may be practiced using any device suitablefor performing the recited steps.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure. In addition, certain method, event, state,or process blocks may be omitted in some implementations. The methodsand processes described herein are also not limited to any particularsequence, and the blocks or states relating thereto can be performed inother sequences that are appropriate. For example, described tasks orevents may be performed in an order other than the order specificallydisclosed. Multiple steps may be combined in a single block or state.The example tasks or events may be performed in serial, in parallel, orin some other manner. Tasks or events may be added to or removed fromthe disclosed example embodiments. The example systems and componentsdescribed herein may be configured differently than described. Forexample, elements may be added to, removed from, or rearranged comparedto the disclosed example embodiments.

In summary, various embodiments and examples of torque-limitingscrewdriver systems and methods have been disclosed. Although thedisclosure has been in the context of those embodiments and examples,this disclosure extends beyond the specifically disclosed embodiments toother alternative embodiments and/or other uses of the embodiments, aswell as to certain modifications and equivalents thereof. Moreover, thisdisclosure expressly contemplates that various features and aspects ofthe disclosed embodiments can be combined with, or substituted for, oneanother. Accordingly, the scope of this disclosure should not be limitedby the particular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims that follow.

The following is claimed:
 1. A surgical torque-limiting screwdrivercomprising: a housing; a motor positioned in the housing and configuredto receive electrical power from a power source; a drive head positionedat a distal end of the screwdriver, the drive head configured to receivea bit that engages a screw and to be rotated by the motor so as toenable the screwdriver to drive the screw into a bone; a current sensorthat samples electrical current drawn by the motor during operation ofthe motor; a controller that, during driving of the screw into the bone:receives signals from the current sensor indicative of the electricalcurrent drawn by the motor; uses the signals to determine a plurality ofdriving torque values, each of the plurality of driving torque valuesindicative of an amount of torque that the screwdriver is applying tothe screw during a respective time period t; stores at least the threemost-recent of the plurality of driving torque values in a memory;compares each of the driving torque values that occur after a deadbandwith a threshold torque value; prevents engagement of a torque-limitingfunction until at least one of the driving torque values that occurafter the deadband is greater than or equal to the threshold torquevalue; permits engagement of the torque-limiting function in response toat least one of the driving torque values that occur after the deadbandbeing greater than or equal to the threshold torque value; reduces therotational speed at which the screwdriver drives the screw in responseto at least one of the driving torque values that occur after thedeadband being greater than or equal to the threshold torque value; andengages the torque-limiting function in response to determining that:engagement of the torque-limiting function is permitted; and at leastthree of the driving torque values that occur after the deadbandconsecutively decrease; wherein the torque-limiting function stops thedriving of the screw by the screwdriver.
 2. The surgical torque-limitingscrewdriver of claim 1, further comprising an override input that sendsa signal to the controller, the override input enabling a user tooverride the torque-limiting function.
 3. The surgical torque-limitingscrewdriver of claim 2, wherein activation of the override input rotatesthe screw a certain amount.
 4. The surgical torque-limiting screwdriverof claim 3, wherein the certain amount is approximately ¼ turn.
 5. Thesurgical torque-limiting screwdriver of claim 2, wherein activation ofthe override input disengages the torque-limiting function for a periodof time.
 6. The surgical torque-limiting screwdriver of claim 5, whereinthe period of time is less than 1 minute.
 7. The surgicaltorque-limiting screwdriver of claim 2, wherein the override inputcomprises a button.
 8. The surgical torque-limiting screwdriver of claim1, wherein the deadband is an amount of time.
 9. The surgicaltorque-limiting screwdriver of claim 8, wherein the deadband is at least50 ms.
 10. The surgical torque-limiting screwdriver of claim 1, whereinthe deadband is an amount of rotations of the screw.
 11. The surgicaltorque-limiting screwdriver of claim 9, wherein the deadband is at least5 rotations.
 12. The surgical torque-limiting screwdriver of claim 1,wherein the time period t is approximately 10 ms.
 13. The surgicaltorque-limiting screwdriver of claim 1, wherein the rotational speed isreduced to less than or equal to 900 rpm.
 14. The surgicaltorque-limiting screwdriver of claim 1, wherein the rotational speed isreduced by a factor of approximately
 4. 15. The surgical torque-limitingscrewdriver of claim 1, wherein the threshold torque value is at least15 N-cm.
 16. The surgical torque-limiting screwdriver of claim 1,further comprising the power source, and wherein the power sourcecomprises a battery in the housing.
 17. A torque-limiting screwdrivercomprising: a housing; a motor positioned in the housing and configuredto receive electrical power from a power source; a drive head positionedat a distal end of the screwdriver and configured to receive a bit thatengages a screw; a transfer assembly connecting the motor and the drivehead such that the drive head is rotatable by the motor so as to enablethe screwdriver to insert the screw into a bone; a sensor that detectselectrical current drawn by the motor during operation of the motor; acontroller that receives signals from the sensor indicative of theelectrical current drawn by the motor and uses such signals to determinea plurality of values of the torque applied to the screw during theinsertion of the screw; the screwdriver configured to stop rotation ofthe screw in response to a torque-limiting condition being satisfied;and the screwdriver further configured to rotate the screw at a firstspeed during a first stage of the screw insertion and to rotate thescrew at a second speed during a second stage of the screw insertion,the second stage being after the first stage and the second speed beingless than half of the speed of the first stage, thereby increasing theinsertion time for the screwdriver to insert the screw into the bone andreducing the angular momentum of the screw during the second stage. 18.The torque-limiting screwdriver of claim 17, wherein the torque-limitingcondition is satisfied when the controller determines that at least fourof the plurality of values consecutively decrease.
 19. Thetorque-limiting screwdriver of claim 17, wherein the torque-limitingcondition is satisfied when a deadband has expired and the controllerhas detected an inflection point in the plurality of values.
 20. Thetorque-limiting screwdriver of claim 17, wherein the first speed isgreater than or equal to 3,600 rpm and the second speed is less than orequal to 900 rpm.
 21. The torque-limiting screwdriver of claim 17,wherein the screwdriver changes from the first stage to the second stagewhen at least one of the torque values that occur after a deadband isgreater than or equal to a threshold torque value.
 22. Thetorque-limiting screwdriver of claim 17, wherein the screwdriver changesfrom the first stage to the second stage after a period of time haselapsed, the period of time beginning at the initial insertion of thescrew into the bone by the screwdriver.
 23. The torque-limitingscrewdriver of claim 22, wherein the period of time is at least 150 ms.